Daily Weather

Jul 18, 2015 10:00 AM HST

Synopsis
A surface high far northeast of the islands will bring trade winds to the area through midweek. The high will be replaced during the middle of the week, which will cause the winds to gradually subside. Look for winds to strengthen again during the latter part of the week. Through the week, showers will be focused over the windward areas, with some afternoon showers over leeward and interior areas when the trades weaken.

Discussion
In general good agreement between the models with the forecast for the week. High pressure far to the northeast of the islands will be replaced by a new high mid week. During that transition, trade winds will weaken, which will allow for some localized land and sea breezes. The resultant ridge remains north of the islands through the transition, but during the second half of the week, the high shifts to be more north of the islands. By the end of the week the trade wind speeds should rebound to more moderate levels.

There is good agreement with the development of a 500 mb low to the northeast of the islands overnight and move to the west. The general path brings the center of the low north of Kauai Monday night. The 500 mb temperatures over the islands with this system remain within normal for this time of year, but it is possible that this system could destabilize the atmosphere again. Earlier forecast update put the slight chance of thunderstorms into the forecast for the Kona slopes tomorrow afternoon. Have left those in place but altered the associated pops.

The global models are in good agreement with a slug of drier air moving over the islands Monday night and Tuesday, which would put some limits on the amount of shower activity. Have made some modifications to the pops through this time period. As the upper low moves west of the islands, the models show an increase in low level moisture moving towards the islands from the southeast, which could increase the shower activity. During this time mid week, winds will be lighter so the showers could form over leeward and interior areas.

More moderate trades are expected to end the week, with showers focused over the windward and mountain areas.

Aviation
Vfr conditions prevail at all taf sites and these conditions are expected to continue through tonight. There may be some local MVFR conditions over windward slopes due to low clouds and SHRA. No airmets are currently in effect.

Marine
A small craft advisory /sca/ is in effect for the typical windier locations near the Big Island and Maui county. Ascat pass last night showed 20 kts, which matched well with hi-res models like the arw and the nmm, which showed a brief uptick expected in the winds today. The SCA goes through 6 am Sunday, but the main focus will be this afternoon. The winds will drop below SCA levels then through mid week, with the next chance for SCA winds coming later in the week.

Surf along east facing shores will be near advisory levels through the next several days due to a number of swells. Current buoy reports match well with the wave watch data and the current forecast so not expecting any changes with that in the short term.

An anticipated intensifying storm system in the south Pacific just east of New Zealand in the next couple of days, will be generating a nice size swell towards Hawaii with the arrival time of Friday night. Please refer to the surf discussion /srdhfo/ discussion for more details.

Watches/Warnings/Advisories
Small craft advisory for waters around Maui including Maalaea Bay and waters south of the Big Island until 6 am HST Sunday.